The roots of the Sensa Feast-day lie in the history of Venice, and more specifically in the episode when Doge Ziani acted as mediator between Pope Alexander III and Emperor Frederick Barbarossa.
 

Legend has it that thanks to a meeting between the Pope and the Emperor on Ascension Day in 1177, and to the Serenissima Republic's diplomatic efforts to bring peace, the Pope bestowed many privileges on the city (the use of the sword, the candle, the seal, ensign, curial seat, silver trumpets, and the concession of an indulgence to Saint Mark on Ascension Day).

This included the act of "marrying the sea", as a sign of Venice's domination at sea and official recognition of the Republic's predominance.